1. Field of the Invention:
The present invention relates to a thin film magnetic head for recording and/or reproducing data on a magnetic recording medium such as a magnetic disk.
2. Description of the Prior Art:
A typical example of conventional thin film magnetic heads is shown here in FIGS. 4(a) and 4(b) of the accompanying drawings. The conventional thin film magnetic head includes a magnetic circuit which is composed of a magnetic substrate made from a magnetic material such as an Mn-Zn ferrite, a gap layer 15, a coil 12, an upper magnetic core 13 and a protective film 14 formed on the magnetic substrate 11 in superposed relation in the order named by using a photolithographic processing of insulating films and conductive films formed by sputtering deposition or vacuum evaporation on the magnetic substrate 11. The magnetic substrate 11 constitutes a lower magnetic core relative to the upper magnetic core 13. As best shown in FIG. 5, the front face of the conventional thin film magnetic head which is adapted to face the recording surface of a magnetic recording medium, not shown, is polished or lapped into a flat surface and the upper magnetic core 13 has a thickness 1 at the front end face.
Since the front end face of the upper magnetic core 13 is flat and has a limited extent in the direction of thickness such as indicated by 1 in FIG. 5, the magnetic flux is able to flow from the front end face of the upper magnetic core 13 over the gap layer 15 into the magnetic substrate 11, thereby reproducing an output other than a desired output.
More specifically, the waveform of an isolated pulse which is reproduced by the conventional thin film magnetic head shown in FIGS. 4(a), 4(b) and 5 includes a distortion appearing in the form of a reverse output C, as shown in FIG. 6. The reverse output C is produced due to the front end face of the upper magnetic core 13 which is flat and has the limited thickness 1 shown in FIG. 5. The position at which the reverse output C is produced is determined by the width of the front end face of the upper magnetic core 13. In addition, the conventional thin film magnetic head has a frequency characteristic curve such as indicated by dash lines in FIG. 7. The frequency characteristic curve includes fluctuations D and E which occur at frequency levels determined by the thickness 1 (FIG. 5) of the upper magnetic core 13 (equal to the width of the front end face of the upper magnetic core 13). In order to reduce the negative influence of the fluctuations, the thickness 1 of the upper magnetic core 13 measured at the front end face is made considerably smaller than the overall thickness of the upper magnetic core 13, as shown in FIG. 5. With this construction, the magnetic flux is likely to saturate due to a sudden increase in the magnetic flux density of the upper magnetic core 13 at a position indicated by B in FIG. 5. Further, even though the thickness 1 of the upper magnetic core 13 at its front end face is considerably reduced, the fluctuations of the reproduced output still occur, affecting the magnetic recording/reproducing characteristics of the thin film magnetic head.